Advanced Self-Healing Polymer-Cement Composites for Geothermal Wellbore Applications Up to 300 °C

Abstract

Polymer-cement composites were formulated using two base cements (cement H and thermal shock resistant cement) and three polymers (a thermoset epoxide-based polymer, Poly(ethylene-co-acrylic acid) zinc salt, and Bisphenol A diglycidyl ether/ Poly(ethylene-co-acrylic acid) and evaluated as potential alternatives to conventional geothermal wellbore cementitious materials. To mimic geothermal conditions, these cement composites were cured at 300 °C and their mechanical properties, including compressive strength, Young modulus, shear bond strength to steel casing, and self-healing and re-adhering (to steel) capability were tested. To test thermal stability the samples were cured at 300 °C for up to 30 days followed by analysis of their mineralogy and chemical composition by X-ray diffraction spectroscopy (XRD), 13C Nuclear Magnetic Resonance spectroscopy (NMR), and total organic carbon (TOC). These tests showed that all polymer composites formulated were thermally stable as supported by the presence of nearly 100% of the original polymer added in samples cured at 300 °C and the presence of all the polymer signals in 13C NMR. Permeability tests performed before and after healing a longitudinal fracture on polymer-cement composites gave lower (post-healing/pre-healing) permeability ratios with respect to base cements which suggests that introduction of polymers result in a composite with self-healing properties. The self-repairing capability is hypothesized to be due to reversible and dynamic polymer-polymer and polymer-cement bonding interactions together with the mobility of these polymers in the cement matrix at high temperature as previously reported for similar composites designed by this grup. Curing two of the best performing polymer-cement composites for a period of 30 days at 300 °C maintained the self-healing capability. These advanced polymer-cement composites with higher mechanical stability, ductility and self-healing capability are promising alternatives to conventional wellbore cement materials for geothermal and fossil energy applications.